<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../vue.global.js"></script>
</head>

<body>
    <div id="app">
    </div>

    <script>
        const app = Vue.createApp({
            data() {
                return {
                    count: 4
                }
            }
        })

        const vm = app.mount('#app')

        console.log(vm.$data.count) // => 4
        console.log(vm.count) // => 4

        // 修改 vm.count 的值也会更新 $data.count
        vm.count = 5
        console.log(vm.$data.count) // => 5

        // 反之亦然
        vm.$data.count = 6
        console.log(vm.count) // => 6
    </script>
</body>

</html>